I'm trying to link a UILabel with an IBOutlet created in my class.

My application is crashing with the following error. What does this mean? How can I fix it?

*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<UIViewController 0x6e36ae0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key XXX.'

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pedrotorres is right. Yes this is right. If you are doing a UITableViewCell, in IB remember to make teh File's Owner to NSObject, and the UITableViewCell'Class to the .h class you defined. – giuseppe
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When you encounter such an issue and the offending key is an action rather than an outlet then most probably you have an outlet which mistakenly references your action function name instead of your outlet variable name. – Alex Yursha
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You should notice that the name of the key in the error message (the OP is calling it 'XXXX') is the name you gave to something in your nib file. That's should help narrow down your search. – kris
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I filed rdar://22105925 asking Apple to make these errors more obvious at build time. :) – jtbandes
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how to actually IMMEDIATELY SOLVE the problem! //allinonescript.com/a/13812660/294884 fantastic tip – Fattie
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I had a custom table row controller class defined as a subclass of the wrong class. Another d'oh moment. – Tom Howard
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One other thing to watch out for is delegate classes. For example your view is of custom class X, but you are using it as an overlay for a UIImagePickerController, for which your controller is a delegate. Your controller will need to have properties for the outlets you referenced. I got caught by this recently. – Andre M
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Okey so my problem had nothing to do with xib files, cause I actually do not use them in my project at all. I was just trying to add a key to an NSDictionary object and got this error. Turned out the way I was adding the objects to the NSDictionary was wrong. – NecipAllef
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I think this comment "If you are doing a UITableViewCell, in IB remember to make the File's Owner to NSObject, and the UITableViewCell'Class to the .h class you defined" needs to be another answer. – Seto Elkahfi

63 Answers 11

  1. You only need to specify IBOutlet once, the IBOutlet label your ivar is unnecessary.
  2. Are you instantiating your NIB using your UIViewController? At some point you should be calling [SecondView initWithNibName:@"yourNibName" bundle:nil];
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This helped! I was getting a key-value coding compliance error about a property from a different view controller. Turns out I was calling -initWithNibName with the wrong nib name. – jlstrecker
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Yes this helped me too.. i was using the UIViewController instead of MyCustomeViewController.. but this is kind of hierarchy issue may be.. the introspection failed because of the miss placed class object.. Thank you anyways – Futur
up vote 733 down vote accepted

Your view controller may have the wrong class in your xib.

I downloaded your project.

The error you are getting is

'NSUnknownKeyException', reason: '[<UIViewController 0x3927310> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key string.'

It is caused by the Second view controller in MainWindow.xib having a class of UIViewController instead of SecondView. Changing to the correct class resolves the problem.

By the way, it is bad practice to have names like "string" in Objective-C. It invites a runtime naming collision. Avoid them even in once off practice apps. Naming collisions can be very hard to track down and you don't want to waste the time.

Another possible reason for this error: when copying & pasting elements from one controller into another, Xcode somehow keeps that link to the original controller, even after editing & relinking this element into the new controller.

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Also do not forget to connect the "view" outlet of the nib to the file owner's view outlet (The view outlet of your custom class inherited from UIViewController). This can be done by control dragging from "File's Owner" under "Place Holders" to "view" under "Objects" and selecting the view outlet. – Nirma
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I've made sure all the class are already set, but the NSUnknownKeyException still comes out :( – Zennichimaro
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I'm not even using Interface Builder, and I'm still getting this error. Any idea what's going on? – sudo
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Never mind. It was because of two things: Xcode was still accessing my Main storyboard even though it was removed from the project, and the simulator had it cached. I highly unrecommend using storyboards or NIBs – they're ridiculously problematic. – sudo
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+1000 for what you say about bad naming practice. This is so obscure to figure out! I had a method called something like 'init....' and the application was crashing randomly all the time, then I renamed it and crashes just stopped. – Ilya Saunkin
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The problem in my case is sometimes -> User Defined Runtime Attributes. If you changed the class for control (and user defined attributes were meant for previous class), those attributes (non-existing for some other class) could throw just that exception. – sabiland
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@TheMuffinMan only 30 minutes? I have already lost one day of work because of this nonsense! – Josh
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@Josh Lol. Everytime I work up the motivation to create a native app in xcode it always ends with me spending a day trying to figure out how to do anything. I'm a c# dev so I've been looking at offerings from Xamarin and Telerik (nativescript) lately. – The Muffin Man
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Swift Language solves a lot of these problems by nailing everything down at compile time, but you lose the flexibility of Objective-C runtime. – TechZen
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Turns out I was inheriting a subclass that already had an outlet for the object, meaning that it had essentially 2 outlets pointing to the same place, causing the crash. – Jacob King
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I had the same issue but fixed it in different way. My project has different build configuration (pointing to different environment) which creates build with different bundle identifier. Somehow one of my cell's module (in Interface builder) was set to specific bundle identifier. I just set it to current-module to make it work. Setting none did not work. – deepax11
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I would also like to point out a "bug" in Xcode that can insert these errors for you. If you make a connection by control-dragging into the class, and then notice that you made an outlet instead of an action (or vice versa), when you delete the code it leaves the connection behind. You have to manually disconnect it in the xib/sb editor. – Maury Markowitz
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quoting: Another possible reason for this error: when copying & pasting elements from one controller into another, Xcode somehow keeps that link to the original controller, even after editing & relinking this element into the new controller. <= that was it for me – MoolsBytheway

Another "not compliant" issue I found was when I managed to have two copies of a class for some reason.

I was adding keys to the wrong copy. Interface Builder still saw the keys and let me hook up to them, but at runtime it was using the other copy of the class that didn't have the new keys.

To find which was the "right" copy I used XCode's cmd-click on the class name elsewhere to jump to the correct copy, then I killed off the bad unused copies (after bringing over my edits from the un-used copy first).

Moral of the story: duplicate class files are bad.

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Updated with project source. – Echilon

I had a similar problem for a project that has two targets (with their own MainWindow XIB). The fundamental issue that caused this error for me was that the UIViewController class wasn't included in the second project's resource list. I.e. interface builder allowed me to specify it in MainWindow.xib, but at runtime the system couldn't locate the class.

I.e. cmd-click on the UIViewController class in question and double-check that it's included in the 'Targets' tab.

I had the same problem and while TechZen's answer may indeed be amazing I found it hard to apply to my situation.

Eventually I resolved the issue by linking the label via the Controller listed under Objects (highlighted in the image below) rather then via the File Owner.

Hope this helps.

enter image description here

I was getting this error with storyboards. The above solution didn't seem to be the problem so I ended up deleting the view controller and adding it back in again (and of course reconnecting the segue and reassigning the class) which fixed it. I don't know what it really was, but I had renamed the associated view controller class shortly before this started, so maybe that had hosed something.

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I got this error again. This time I created a new empty table view controller with my class assigned to it, leaving the non-working one alone, and moved the segue to it. This worked. I then slowly copied every element in the view over until it failed again. This time the problem turned out to be I had assigned some "User Defined Runtime Attributes" for a picker (I was thinking I could use them to initialize the picker so I wouldn't have to do it in code, no idea if that's possible). Removing that fixed the problem. This error is really horrible, I hope it's improved in a future release! – Symmetric

You may have a bad connection in your xib.

I've had this error many times. While TechZen's answer is absolutely right in this case, another common cause is when you change the name of a IBOutlet property in your .h/.m which you've already connected up to File's Owner in the nib.

From your nib:

  1. Select the object in IB and go to the 'Connections Inspector'.
  2. Under 'Referencing Outlets' make sure that your object isn't still connected to the old property name... if it is, click the small 'x' to delete the reference and build again.

    example 1

Another common cause if you are using Storyboard, your UIButton might have more then one assignings (Solution is almost the same as for nib):

  1. Open your storyboard and right click the UIButton
  2. You will see that there is more than one assign/ref to this button. Remove one of the "Main..." greyed windows with the small "x":

    example 2

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Thanks! In my case I had 2 outlets to the same view, and getting rid of the old one and hooking up the view to the new one ended the exception. – Mark Patterson
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mine was duplicated twice. I began disconnecting each one after i dragged and dropped from a Pro version ( from a Lite version ) thinking it was hanging onto connections in the other project. When i came across the duplicate, and it took 3 clicks to make the disconnection, i sincerely wished i done that 3 days earlier. Oh well- such is the life of a dev. – aremvee
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I had the problem that UIButton was having more than one assignings. This solved my issue. – mythicalcoder
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I had this problem too. Don't forget to check outlet connections in particular views instead of only superviews. In my case, superviews weren't showing the wrong connections =/ – Augusto Carmo
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I had a similar error where I connected a button outlet to a the wrong ViewController swift file whose page would not have been created yet using the GUI – brw59

I had to delete the app from the simulator/iPhone to get rid of this error.

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+1 this fixed it for me. I was cleaning up some code that used IB. When I deleted a button from the code the error kept popping up even when this button was not referenced at all in the nib files (at least that I could see). – SundayMonday
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I find this is necessary if you are debugging two applications that happen to have the same name. – Anton
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Yep, it seems that something from the XIB is cached on the simulator, which is a pain if you're testing upgrades since you actually don't want to have to delete the old app. – Carlos P
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I had this problem deleting my XIB file. This fixed the problem. – balboa
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If deleting app does not work, try deleting the XCode DerivedData folder. which can cache an incorrect xib file. Open XCode -> Preferences -> Locations -> Open the DerivedData folder and drag it to Trash. – Philip Fung

I got the same problem. I did resetting the simulator. Removing and adding button control. and finally made a clean. :) Thanks to stack overflow. Some how my code became ok and starting working.

If it is an iPhone only app, not a universal one, make sure the following field is empty:

Targets > Summary > iPhone/iPod Deployment Info > Main Interface

If you specify an xib there it crashes.

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Yep, that was it for me. While flailing around to add a new startup view controller I set this to the new class/nib. After hooking up the view outlet I was hitting this error. Clearing this field fixed it. – terriblememory
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This worked for me. Note that I also had to delete the old version from the device/simulator for it to work. – jimt
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Thanks - this was my problem. I had renamed my iPad storyboard file and did not update in my project's prefs. – RobertJoseph
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Thank you! This solved it for me. (I had to delete the app from the simulator after changing the Main Interface field to be empty. Simply changing that field didn't force the simulator to break the cache.) – snipe
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I remembered that I changed things from a universal app to a iphone only app and this fixed the error! – Justin
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it work for me. Thanks – Thiago Arreguy
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This was my solution. – Teofilo Israel Vizcaino Rodrig

That might be the case of referencing a component from Xib Interface that you have renamed or delete. Re-referencing works for me.

Usually when this happens to me, @TechZen's answer does the trick. Yesterday, however, I spent an embarrassingly long time mucking with storyboard connections only to discover that the problem was in my code.

I have a custom view controller that handles various layouts in my storyboard, but one of the layouts needed a special label not used by the others. So I created a subclass like so:

@interface MyViewControllerSubclass : MyViewController

Then I added a private property in MyViewControllerSubclass.m:

@interface MyViewController ()
@property (weak, nonatomic) IBOutlet UILabel *crashesApp;
@end

Xcode happily allowed me to connect this IBOutlet, yet every time the view would load, the app would crash with the old "not key-value compliant for the key 'chrashesApp'".

The solution, which is semi-obvious in retrospect, was to change the private category to use the correct name, i.e., that of the subclass:

@interface MyViewControllerSubclass ()
@property (weak, nonatomic) IBOutlet UILabel *noMoreCrashing;
@end

I had the same kind of problem. I created a tableviewCell in a XIB file and was getting that kind of error. My problem was that I defined the "File's Owner" class to be my cell view controller. I just took it out and set the cell's class (on the xib file click the border of the cell, go to the third tab on the right panel and where it says class chose your view controller).

Also try cleaning your code.

I just had this issue in my duplicated project and solved by checking 2 places:

1- Make sure you have the .m file in the list -> Project - Build Phases - Compile Sources
2- After that, go to interface builder (probably this is an error occures with only IB) and unlink all properties, labels, images, etc... Then re-link all. I have realized that I've removed an attribute but it was still linked in IB.

Hope it works for some.

Same issue presented. My solution was to put the correct storyboard value in the Main Storyboard drop down. I had renamed mainstoryboard.storyboard, but not reset the deployment info.

Another one cause of this situation is that you declare this property implemented as @dynamic, but class can not find it in parent class.

This problem also happens if you want to design a small subview in a separate XIB file in Interface Builder, and in IB you set it to the same class as the parent view.

If you then show it like this:

UIViewController *vc = [[UIViewController alloc] initWithNibName:@"NameOfTheSubviewNibFile" bundle:nil];
[self.view addSubview:vc.view];

The view will appear, but if it's got IBOutlets connected to its File Owner, you'll get the error message. So, this should work instead:

  1. In your the parent view's code, declare an IBOutlet UIView *mySubview to reference the view in the subview's nib file
  2. In the subview's nib file, connect the File Owner to the view, and set it to mySubview
  3. show it by doing:
[[NSBundle mainBundle] loadNibNamed:@"NameOfTheSubviewNibFile" owner:self options:nil]
[self.view addSubview:mySubview];

and you will be fine!

Check if you have stray Referencing Outlets by selecting the offending object in the Storyboard/xib interface and opening the Connections Inspector (View->Utilities->Show Connections Inspector). If you do remove the unwanted connections and you should be good to go.

This error indicates that an already connected Interface Builder object is removed/renamed in its owner's source (File's Owner).

Control-click on the Files's Owner in the Interface Builder if you see a exclamation mark you need to fix that.

In the picture below you can see that "aRemovedView" has an exclamation mark on its right, that's because I removed the IBOutlet view object while it was already connected in the IB.

enter image description here

This gives the following error: Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key aRemovedView.'

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Thank you! This fixed it for me. I've been having this issue for a long time and didn't know how to fix it other than starting over from scratch. This was it, deleted IBOutlets from the view controller, but didn't know they were still referenced/linked in the owner (in this case "View Controller" in interface builder - Xcode 6). – Ira Herman

I deleted the property from the header file. I couldn't find any reference to it but the debug error was still referencing it. I found that the nib file still had a reference to it. I deleted the block that referenced it and everything was fixed.

In Project Navigator,

Find the Nib (xib) file. Right click and View Source. I deleted the the following full section

<object class="IBConnectionRecord">
    <object class="IBCocoaTouchOutletConnection" key="connection">
        <string key="label">DeleteLabel</string>
        <reference key="source" ref="372490531"/>
        <reference key="destination" ref="774585933"/>
    </object>
    <int key="connectionID">20</int>
</object>

This happens to me when my view controller originally had an .xib file, but now is created programmatically.

Even though I have deleted the .xib file from this project. The users iPhone/iPad may contain an .xib files for this viewcontroller.

Attempting to load an .xib file usually causes this crash:

Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<UIViewController 0x18afe0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key welcomeLabel.'

Solution when creating it programmatically may be this:

-(void)loadView {
    // Ensure that we don't load an .xib file for this viewcontroller
    self.view = [UIView new];
}

I found another possibility that may cause the issue.

When using "initWithNibName" method with the wrong xib name, it will lead to this kind of crash too.

Such as you choose to change a xib file's name, and then foget to change the name used in "initWithNibName" method to the same name.

I remember having a similar problem in the past, I solved it by changing the line:

_vicMain = [[UIViewController alloc] initWithNibName:@"vicMainScreen" bundle:nil];

into:

#include "vicLogin_iPad.h"       // This is the H file of the class holding the code for
                                 // processing all the IBOUtlets for the Login screen
.
.
.

_vicMain = [[vicLogin_iPad alloc] initWithNibName:@"vicMainScreen" bundle:nil];

Notice that I was initially declaring UIViewController to init my _vicMain, after using a pop-up window on top, I realised that both are using the same UIViewController.

By:

1) INCLUDing your class (of the sub-view), along with the same module that is doing the above _vicMain (which is a view controller object/variable) i.e. it's "vicLogin_iPad.h" in my case , and:

2) Use the your custom constructor to declare the object (i.e. instead of "xxx = [UIViewController alloc] ... ", you use "xxx = [vicLogin_iPad alloc] ... " instead.

the problem is resolved.

I hope this helps as it was a pain to pinpoint with the lack of details from the error message...

Regards Heider Sati

I had exact same error message and thanks (!!) to Kira from http://www.idev101.com I was able to solve the challenge. I only found her site after googling and stacking over all these threads. I'm now posting here for the next one that comes to StackOverFlow and has the same challenge I had since that person will most likely come to this thread over Google.

I realized, that I wrongly made this:

UIViewController *deviceViewController = [[UIViewController alloc] initWithNibName:@"DeviceViewController" bundle:nil];

Instead of THIS:

DeviceViewController *deviceViewController = [[DeviceViewController alloc] initWithNibName:@"DeviceViewController" bundle:nil];

Where

DeviceViewController

Was the name of my Class also known as

DeviceViewController.h 
DeviceViewController.m

You'll have to

"import DeviceViewController.h"

in your implementation (.m File) where you want to call e.g. another UIViewController.

I am absolutely not sorry if I am only stating the obvious for beginners like me and may get down votes as this is not exactly related to the question but I was searching 4 (?!?) hours straight now for the answer to these error message. If I can spare this to 1 or 2 people that'd be great :)

PS: For those interested in how the code continues for loading the other UIViewController:

    [self presentViewController:deviceViewController animated:YES completion:nil];
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THANKS for all the steps there, I was using Xcode 5 and didn't really know how to manually add a nib as you can only add storyboard by default.... I got some instructions but non as detailed as yours. Really helped!! – Pittfall

I encounter the same error log when dealing with my tableview cell. I found that my UILabels have duplicated referencing outlets(you could check it out in the reference inspector) to both the file's owner and my cell's class. Things get well when I delete the reference to the file's owner.

This was happening to me only when debugging on a device (iPhone). The iOS Simulator was working OK. Doing a "Product->Clean" from Xcode seemed to solve the problem, but I have no idea why.

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This solve my problem. tsk2x almost 3 days of headache. – user3818576
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It does provide an answer to the question. Something got messed up in Nib and doing a clean solved it. I read and tried all of the above to no avail and then did the clean, and after 1 hour of trying to fix it, Maj's solution fixed it. I would've loved to see what in the XML could've caused this but I've moved on. – LevinsonTechnologies
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This does indeed solve the issue - I tried numerous suggestions above and only did the project clean fix this error that suddenly started occurring. Ugg... – DustinB
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This fix my problem, I tried lot of above suggestions. Seems strange! – Naveen Shan

I had the same error in yet another slightly different form:

In interface builder, I have a navigation controller with a custom subcontroller. The class name of this was set correctly, however the NIB name (select subcontroller, go to Attributes Inspector) was set to the wrong file (basically to one of a different target). Resetting this to the correct filename solved the issue.

I had this problem too. I had copied a view with an IBOutlet from one xib file to another xib file. And even though I had removed the old reference and create a new reference, this error was still occurring.

I ended up restarting xcode to fix this problem.

I had this error when I was trying to implement a custom ViewCell for a table. When I highlighted View controller for the XIB and connected to the elements in the CellView caused the error " this class is not key value coding-compliant for the key" once I deleted these it got rid of the error.

Delete the connections in the below image. Delete the connections in inspector when File Owner is highlighted

Just make sure that you only have the connections with the Table View Cell. To check click on table view cell and in INSPECTOR look for your connections.

The connection should be in here when Table View Cell is highlighted

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This did it for me, thanks so much. I x'd out the connections when "File's Owner" was selected in the left column, then selected my custom cell and reattached them. Success! – Rogare
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Even with xcode7 this works, just use the right panel "Connections inspector". Remove the outlet from the tableviewcell and from the label, then re-add it and everything should work. – lifeisfoo
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This works but you need to make sure FileOwner didn't get set!! File owner should remain NSObject. //allinonescript.com/questions/13793162/… – user2704776

enter image description here enter image description here

My fix was similar to Gerard Grundy's. In creating a custom UITableViewCell using an XIB, I had mistakenly applied the Custom Class name to the File's Owner instead of to the UITableViewCell. Applying the class to the UITableViewCell on the canvas and connecting my IBOutlet properties to it solved the issue.

In my case,

[[NSBundle mainBundle] loadNibNamed:@"NameOfTheSubviewNibFile" owner:self options:nil]

was the reason.

replacing this with initWithNibName, resolved.

In my case, this was caused by referencing the wrong Nib:

BMTester *viewController = [[BMTester alloc] initWithNibName:@"WrongNibName" bundle:nil];
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Happens to me when I rename the view controller's class and forget that the the nib name needs to change too. Since the nib name is just a string, there's no compiler error. – kris

in my case it was an error in the storyboard source code, follow these steps:

  1. first open your story board as source code
  2. search for <connections>
  3. remove unwanted connections

For example:

<connections>
    <outlet property="mapPostsView" destination="4EV-NK-Bhn" id="ubM-Z6-mwl"/>
    <outlet property="mapView" destination="kx6-TV-oQg" id="4wY-jv-Ih6"/>
    <outlet property="sidebarButton" destination="6UH-BZ-60q" id="8Yz-5G-HpY"/>
</connections>

As you see, these are connections between your code variables' names and the storyboard layout xml tags ;)

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worked for me :) – Navneet Krishna

I had the same symptom. The root cause was that the "Target Membership" for my source file was not set to the correct target. I assume that means my class wouldn't get built and included in my app.

To correct it:

  1. Highlight your .m file.
  2. In the right pane, select the File Inspector.
  3. Under the "Target Membership" section, make sure the appropriate build target is checked.

Hope this helps somebody out there.

This error is something else!

Here is how i Fixed it. I'm using xcode Version 6.1.1 and using swift. I got this error every time my app tried to perform a segue to jump to the next screen. Here what I did.

  1. Checked that the button was connected to the right action.(This wasn't the problem, but still good to check)
  2. Check that the button does not have any additional actions or outlets that you may have created by mistake. (This wasn't the problem, but still good to check)
  3. Check the logs and make sure that all the buttons in the NEXT SCREEN have the correct actions, and if there are any segues, make sure that they have a unique identifier. (This was the problem)
    • One of the segues did not have a unique identifier
    • One of the buttons had an action and two outlets that I created by mistake.
    • Delete any additional outlets and make sure that you the segues to the next screen have unique identifiers.

Cheers,

This has already happened to me twice.

The solution was remaking the whole storyboard since I copied it from another one (because it was almost the same)

This also happens to me when an UI label or other UI element is referenced by two variables in the view controller class and I delete one of the variable.

Looking over the other answers it seems like there are a lot of things that can cause this error. Here is one more.

If you

  • have a custom view
  • added an @IBInspectible property
  • and then later deleted it

Then you may also get an error similar to

Failed to set (xxx) user defined inspected property on [Your Custom View] ...: this class is not key value coding-compliant for the key [xxx].

The solution is to delete the the old property.

enter image description here

Open the Identity inspector for your class, select the property name under User Defined Runtime Attributes, and press the minus button (-).

Sometimes swift file are not added or removed from target, go to target-->Build setting --> compile Sources --> see if any required swift class file is missing or not . In my case Application was crashing due to swift source file not present in compile.

"Module" property of View Controller in the Identity Inspector might be different than what you expected. Also make sure that new classes are added to your target list.

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voting up since it was so in my case. I'm using Swift and Storyboards. When I created a new build target (to make a build variant) the app didn't work in the new variant while the first one worked OK. The app crashed on a View Controller where the module name was somehow set to module from the first target, while in working View Controllers it was Current - <module name here>. You need to erase the module name there in this case. – Mixaz

Another tricky case:

In IB added ViewController to storyboard, deleted its view and set Custom Class to "MyViewController" so view is instantiated from MyViewController.xib

Specifying Storyboard ID the same "MyViewController" causes exception.

Changing Storyboard ID to some different name resolves the issue.

I had this problem with swift classes after upgrading to xcode7. Solved it by using the @objc directive:

@objc(XXXViewController) class XXXViewController

In my case. I didn't have missing outlets in xib-files after merging.

Shift + Command + K

solved my problem. I cleaned my project and rebuilt.

Just to add to this, because I was getting this error as well. Going through all these answers most seem to apply to working with the UI and storyboard stuff. I know the original poster did seem to be working with the UI but when searching for possible reasons for this error mostly all questions lead back to this question with those others being closed as duplicates or simply having issues with connecting things in a storyboard so I will add my solution.

I was working on coding a web service in Swift 2. I had built all the needed proxy objects and stubs. As I looped through the returned XML I was dynamically instantiating my objects, which all came from NSObject and using setValue:forKey on them. Every time setValue:forKey tried to set a property it blew up with this error.

I had a switch statement for each type I was dealing with (e.g. Bool?, CShort?, String?) and for each XML node I went through and checked what the type was on the object and then converted the value to that type and attempted to set it with setValue:forKey.

Eventually I started commenting out all these setValue:forKey lines and found that my default switch statement case did work for String?.

I finally figured out that you can't use optional swift types with setValue:forKey unless they have a direct mapping to an Objective-C type like String? or NSNumber?. I ended up changing all CShort? types to NSNumber? since that has a direct mapping. For Bool? in my case it was fine for me to just use Bool and initialize it to false. Others may not have that luxury.

Anyway what a headache that was so hopefully this helps someone else who has a similar problem and keeps getting redirected to this question and saying to themselves, "I am not doing anything in UI!!".

So lastly to reiterate one more time Key-Value Coding does not work with optionals. Below I ended up finding somewhere but I forget where so to whoever posted this I apologize and would give credit if I remembered where I found this but it saved my life:

You cannot use KVC on an Optional Int property, because KVC is Cocoa / Objective-C, and Objective-C cannot see an Optional Int - it is not bridged to Objective-C. Objective-C can only see types that are bridged to Objective-C:

class types that are derived from NSObject

class types that are exposed with @objc

Swift structs that are bridged

I had the same issue.This happened with my project because I changed my product name but in interface builder I had the old name as Module, this leads to crash so be sure to check all the xib module name also has been changed or not.

You may have outlets to UI Element but not IBOutlet property in .h File

For all UI element in Connection Attribute check outlets and it corresponding property in .h header file.

May be missing one or more property entry in .h file.

Along with other issues that you can see in other answers. The way I created this error for myself was that I started a project from scratch and begin by deleting the initial scene of my storyboard and then pasted a scene from another project into my storyboard.

There is no problem in doing that. You only need to add an entry point of your storyboard i.e. check the is initial View Controller on which ever view controller you like. Otherwise it will be a gray scene and throw you an error.

enter image description here

"this class is not key value coding-compliant for the key" I know its a bit late but my answer is different so I thinks it needs to be posted, I was pushing the second controller in wrong way, Here is sample

Wrong Way to Push Controller

UIViewController* controller = [[UIViewController
 alloc]initWithNibName:@"TempViewController" bundle:nil];
         [self.navigationController pushViewController:controller animated:true];

Correct way

TempViewController* controller = [[TempViewController
 alloc]initWithNibName:@"TempViewController" bundle:nil];
         [self.navigationController pushViewController:controller animated:true];

I did not found any answer like above so may be it can help some one having same issue

I had this happen when i had a UIView linked into a storyboard and connected IBOutlet like:

@property (strong, nonatomic) IBOutlet UIView *someView

but later on, i made the UIView into a custom class but forgot to change the class name of this IBOutlet defined above. its a strange error because if the custom view has no subviews it doesnt complain, but as soon as there are subviews it shows the error stated in the question but on one of the subviews and not the outer UIView where the problem actually exists. had me deleting and readding all the subviews trying to find the problem, when in fact had nothing to do with the subviews

I had the same issue when I was using the main storyboard as the launch screen file. I guess if you are using a storyboard as the launch screen file, it shouldn't be connected to the view controller as it won't have been loaded yet.

I ran into the same problem for a different reason: I was using the main storyboard as the launch screen file. I guess if you are using a storyboard as the launch screen file, it shouldn't be connected to the view controller as it won't have been loaded yet.

It could mean you're trying to use a sort descriptor without an atsign at the beginning. As in:

[array valueForKeyPath:@"distinctUnionOfObjects.self"]

Which must actually be:

[array valueForKeyPath:@"@distinctUnionOfObjects.self"]

You may need to delete the outlet , recreate it by drawing form IB to .H file.

If you have a custom UIViewController subclass with IBOutlets that are causing problems the only set of steps I found to actually get rid of the error were

.1 Change the class to UIViewController

.2 Disconnect all the outlets (they will all have the yellow warning triangle now) - it may be enough just to disconnect the problematic outlet(s).

.3 Do all the standard steps - ↑⌘K, delete Derived Data (, prayer mats, worry beads)

.4 Launch the app - go to the problematic scene.

.5 Kill the app, go back to Interface Builder change the class back to your custom class name.

.6 Reconnect your outlets.

Launch the app & this will normally have cleared up the key-value compliance issues.

Did you leave your picker object unconnected?

lol 54 answers and not one of them is my solution. Talk about a common error.

In my case it was because I had a picker object on my VC and had not set an outlet and action for it.

I often leave buttons etc unconnected when I am just looking to see how the layout looks. But it seems you cannot do this for a picker.

Just pay attention if you're trying to observe a value that doesn't exist.

This happened to me simply as I was observing the "Text" property of a text field when I was supposed to be observing the "text" property instead.

The cause of my trouble, was that I duplicated a storyboard file (outside of Xcode if I recall correctly), then all view controllers in the duplicated file had same object-ID as in the original file. The remedy is to copy-pasted the view controllers, and they will then get a new object-ID. You can see the object-ID in the Identity Inspector.

I had the same issue, and the cause was due to specifying a Module in Interface Builder (as opposed to leaving it blank). So, when I was using either a different module than the one I set, the app would crash :S ... hope this helps someone else, as my issue was not due to a broken or out-of-date outlet!

Make sure you add the custom class' (even empty) implementation in the .m file like:

@implementation MySubclass
@end

I had this problem with storyboard and swift class for ui view controller. Solved it by using the @objc directive:

@objc(MyViewController) class MyViewController

Sometimes this has to do with your "Inherit From Target" That value has to be set. With single target apps you can just select Inherit From Target. If you have more then one target select the desired target. enter image description here

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This answer helped me for a specific case. I have to continu working on an old obj-c project with multiple target. I create a custom UITableViewCell in Swift and I had the same error. By enabling "Inherit From Target" it worked. Thank you! – Cédric
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this is the real fix. You saved my life – Deniz Yazar
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The module is not always set correctly; e.g. if you fill in the class name before actually creating the class. – Johan

My problem started after i changed the Target name.

My own custom UI classes had the Module name set to the old target name.

I changed the target name to the new one and it works fine now.

It can come from the fact that you have control dragged and created an outlet or action, and forgot to delete it. Even if you deleted the code, or even if you have made enough cmd+Z, you'll need to go in the connection inspector of your storyboard and see if the action or outlet you created is still here or not.

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Thanks! I'm a n00b on Xcode and took me a while to find the rogue links. In Xcode 9.2, you can right click on the element in the storyboard view and check the "Referencing outlets". – kunigami

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